# Tag Info

Fixing again some typos of yours, we know that in HJM under the risk-neutral measure $$f(t, T)=f(0, T)+\int_0^t\left(\sigma(s, T) \int_s^T \sigma(s, u) \,du\right)\,ds+\int_0^t \sigma(s,T)\,dW_t^*$$ always holds. This implies $$h(T-t)+\int_0^tb(s)\,ds=f(0,T)+\int_0^t\left(\sigma(s, T) \int_s^T \sigma(s, u) \,du\right)\,ds\,.$$ Taking the derivative w.r....